Method for the manufacture of float glass

ABSTRACT

Glass having a shaded characteristic, for example a shaded windscreen, is manufactured by maintaining a body of molten material for modifying the glass against a surface of the moving glass and controlling variation in the treatment of the glass in a lateral direction with respect to the direction of movement. The method involves the provision of a locating member which is shaped to maintain the molten body with a configuration in which its dimension in the direction of glass advance is widest at its center and tapers toward both its ends. The glass is subsequently cut longitudinally through its center to produce a pair of shaded component glass ribbons.

O Umted States Patent [151 3,647,407

Robinson 1 Mar. 7, 1972 [54] METHOD FOR THE MANUFACTURE 3,215,345 II/1965 Ferguson ..65/97 X OF FLOAT GLASS 3,467,508 9/1969 Loukes et al......65/99 X [72] inventor: Albert Sidney Robinson southpon, 3,505,0474/1970 Plumat ..65/30 gland Primary Examiner-S. Leon Bashore [73]Assignee: Pilkington Brothers Limited, Liverpool, AssistantExaminer--Robert L. Lindsay England Attorney-Morrison, Kennedy &Campbell '1 196 [22] F1 ed Mar 3 9 ABSTRACT 21 A l. N 803,565 l 1 PP 0Glass having a shaded characteristic, for example a shaded windscreen,is manufactured by maintaining a body of molten 8 Aplfllcamm Pnonty D818material for modifying the glass against a surface of the mov- Mar. 61968 Great Britain [0,937/68 glass and cntrlling in the treatment theglass in a lateral direction with respect to the direction of move- 52US. Cl. ..65/30, 65/87, 65/99 A, The method involves the Provision of alocating 5/1 2 R, 117/124 A member which is shaped to maintain themolten body with a [51] Int. Cl. ..C03b 18/00 wnfiguration in which itsdimension in the direction of glass [58] Field of Search ..65/30, 65,97, 99, 182; a v nce is widest at its center and tapers toward both itsends. 204/DIG. 8; 117/ 124 A The glass is subsequently cutlongitudinally through its center to produce a pair of shaded componentglass ribbons. [56] References Cited 1 Claim, 3 Drawing Figures UNITEDSTATES PATENTS 2,232,019 2/1941 Beckwith ..,,..20 4/2 0 3/= 1 I Y l J LJ -7- 35 PATENTEIJMAR 7 I972 SHEET 1 [IF 2 ALBERT SIDNEY ROBINSONPATENTEBMAR H972 3, 47,407

' sum 2 OF 2 I nuenlor ALBERT S IDNEY ROBINSON y I i/ g wya METHOD FORTHE MANUFACTURE OF FLOAT GLASS BACKGROUND OF THE INVENTION Thisinvention relates to the manufacture of glass having shadedcharacteristics, for example, glass which in different regions exhibitsdifferent transmittance or reflectivity. Such glass is particularlyuseful for making motor vehicle windscreens, when it can be arrangedthat the upper region of the windscreen transmits less light than thelower region thereof, so that solar radiation passing through thewindscreen is attenuated, while forward visibility through thewindscreen is virtually unimpeded.

An object of this invention is to provide an improved method andapparatus for use in the manufacture of glass having predeterminedshaded surface characteristics.

SUMMARY According to the invention a method of manufacturing glasshaving a shaded characteristic comprises supporting the glass to bemodified, maintaining against a surface of the glass a body of moltenmaterial which is effective to produce the desired characteristics whenincorporated in the glass, effecting relative movement between the glassand the body, and effecting a controlled variation of the treatment ofthe glass by said body in a lateral direction with respect to thedirection of said relative movement, by varying in the said lateraldirection the efficacy of the body of molten material to introduce saidcharacteristics into the glass.

The preferred method of operating the invention is by maintaining amolten metal body adjacent the upper surface of an advancing ribbon offloat glass by causing the body to cling to a locating member having adesired tapered shape to be imparted to the body, and causingelectrolytically ionic migration from the molten metal body into theglass surface. The glass is modified so that the light transmission is amaximum in a central region of the glass and decreases towards thelateral margins of the glass, and after modification the glass is cutcentrally along its length in the direction of said relative movement toprovide two windscreen glasses in the lateral width of the glass.

The invention also provides apparatus for use in the manufacture offloat glass having shaded characteristics, comprising glass supportmeans, thermal regulators associated with the support means to controlthe temperature of the glass, means for maintaining againsta heatedsurface of the glass an elongated molten metal which is effective toproduce the desired characteristics when incorporated in the glass,means for effecting relative movement between glass supported by thesupport means and the body of molten material, the means for varying thetreatment of the glass by said molten body laterally of the direction ofsaid relative movement. The means for maintaining the molten bodyagainst the surface of the glass may be so shaped that the length ofsaid body in the direction of said relative movement varies laterally ofthat direction toward the ends of the body.

BRIEF DESCRIPTION OF THE DRAWINGS A DESCRIPTION OF THE PREFERREDEMBODIMENTS Referring to FIG. I and 2 of the drawings a forehearth of acontinuous glass melting furnace is indicated at l and a regu latingtweel at 2. The forehearth ends in a spout 3 comprising a lip 4 and sidejambs 5 one of which is shown in FIG. 1. The lip 4 and side jambs 5together constitute a spout of generally rectangular cross section.

The spout 3 is disposed above the floor 6 of an elongated tank structureincluding sidewalls 7 joined together to form an integral structure withthe floor 6, an end wall 8 at the inlet end of the tank and an end wall9 at the outlet end of the tank. The tank structure holds a bath ofmolten metal 10 whose surface level is indicated at 11. The bath is forexample a bath of molten tin or of a molten tin alloy in which tinpredominates and which has a specific gravity greater than that of theglass.

A roof structure is supported over the tank structure and the roofstructure includes a roof l2, sidewalls l3 and integral end walls 1 1and 15 respectively at the inlet and outlet ends of the bath. The inletend wall 14 extends downwardly close to the surface 11 of the moltenmetal to define with that surface an inlet 16 which is restricted inheight and through which molten glass is advanced as will be describedbelow.

The outlet end wall 15 of the roof structure defines with the outlet endwall 9 of the tank structure an outlet 17 through which the ultimateribbon of glass produced on the bath is discharged onto driven conveyorrollers 18 mounted outside the outlet end of the tank structure anddisposed somewhat above the level of the top of the end wall 9 of thetank structure so that the ribbon is lifted clear of the wall 9 fordischarge through the outlet 17.

The rollers 18 convey the ultimate ribbon of glass to an annealing lehrin well-known manner and also apply tractive effort to the ribbon ofglass to assist in advancing the ribbon as it glides along the surfaceof the bath 10.

An extension 19 of the roof structure extends up to the tweel 2 andforms a chamber having sidewalls 20 in which the spout 3 is disposed. I

Molten soda-lime-silica glass 21 is poured onto the bath 10 of moltenmetal from the spout 3 and the tweel 2 regulates the rate of flow of themolten glass 21 over the spout lip 4. This lip is vertically spaced fromthe surface 11 of the bath so that there is a free fall of the moltenglass 21 through a distance of a few inches, which is exaggerated inFIG. 1, to the level of the bath surface 11. This free fall is such asto ensure the formation of a heel 22 of molten glass behind the glass 21pouring over the spout, which heel extends back to the inlet end wall 8of the tank structure.

The temperature of the glass as it is advanced along the bath isregulated from the inlet end down to the discharge end by temperatureregulators 23 immersed in the bath 10 and temperature regulators 24mounted in the headspace 25 defined by the roof structure over the bath.A protective gas is supplied to the headspace through ducts 26 which areprovided at intervals in the roof 12. The ducts 26 are connected bybranches 27 to a header 28 which is connected to a supply of protectivegas and preferably the protective gas contains a reducing constituentfor example a proportion of hydrogen. Thus a plenum of protective gas ismaintained in the substantially closed headspace, and there is outwardflow of protective gas through the inlet 16 and the outlet l7 from theheadspace.

The temperature of the molten glass delivered to the bath is regulatedby the temperature regulators 23 and 24 as the glass is advanced alongthe bath so as to ensure that a layer of molten glass 29 is establishedon the bath. This layer 29 is advanced through the inlet 16 and duringthis advance there is unhindered lateral flow of the molten glass underthe influence of surface tension and gravity to the limit of free flowof the molten glass, until there is developed on the bath surface fromthe layer 29 a buoyant body 30 of molten glass which is then advanced inthe form of a ribbon 32 along the bath 10. The width of the tankstructure at the surface level of the bath I0 is greater than the widthof the buoyant body 30 of molten glass so that there is no hindrance tothe initial lateral flow of the molten glass.

in order to impart desired transmission or reflecting characteristics tothe upper face of the ribbon 32 of glass by the method according to thisembodiment of the invention, a body of molten electrically conductivematerial is maintained by surface tension forces against a surface ofthe glass and the glass is moved beneath said molten material.

A shaped electrode bar 31 is mounted transversely of the ribbon 32 ofglass which is being advanced along the bath ll) of molten metal. Thebar 31 is mounted just above the upper surface of the glass so that agap, for example of about 3-4 mm., is left between the bottom of the barand the path of travel of the upper surface of the glass. The bar 31 ismaintained in position by a connection rod 33 which extends into theheadspace 25 over the bath through the sidewall of the tank and isconnected to the center of the bar 31. Electricalinsulating means (notshown) may also be provided for assisting in locating the electrode bar31 accurately adjacent to the upper surface of the glass ribbon 32.

The bar 31 is widest at its center and tapers away towards both ends, togive maximum treatment at the center of the ribbon, shaded away to aminimum or no treatment at the margins of the ribbon, as describedbelow.

The rod 33, as well as serving for the mounting of the shaped electrodebar 31, is also an electrical conductor enabling electrical connectionof one electrode of a DC electrical supply to the electrode bar 31.

The electrode bar 31 acts as a locating member for an elongated body 36of molten electrically conductive material which clings to the lowersurface of the bar 31 and is confined between that surface and the upperface of the glass ribbon 32. The clinging of the body 36 of moltenmaterial to the electrode bar 31 ensures the location of that bodyrelative to the glass and prevents forward movement of the moltenmaterial with the glass.

The invention can be carried out near to the hot end of the bath asillustrated in FIGS. 1 and 2 where the temperature of the glass is forexample in the range of 850 to 900 C., and where the glass is in aplastic condition.

A second electrode 37 dips into the bath of molten metal alongside thepath of travel of the glass and this electrode 37 is mounted on aconnection rod 38 which extends through the sidewall 7 of the tankstructure and is connected to the other terminal of the electrical DCsupply. Alternatively an alternating current supply may be connectedacross the electrode bar 31 and electrode 37.

The electrical connection to the supply circuit is in such a sense thatthe electrode bar 31 and the electrode 37 act effectively as the anodeand cathode respectively of an electrolytic circuit comprising theelectrode bar 31, the body 36 of molten material, the glass ribbon 32,the bath of molten metal and the electrode 37. The passage of currentthrough the glass ribbon 32 causes controlled migration of an elementfrorn'the confined body 36 of molten material into the top surface ofthe glass, thereby effecting a predetermined change in the surfacecharacteristics and therefore in the transmission characteristics, ofthe glass, as will be described below.

The electric current passing through the glass between the body 36 ofmolten material and the bath of molten metal 10 is regulated in relationto the speed of advance of the ribbon 32 of glass so that the migrationand entry of an element into the top surface of the ribbon of glass canbe accurately controlled, so controlling the intensity of the change incharacteristic of the surface of the glass.

Many molten electrically conducting materials may be employed in thebody 36 for effecting the change in transmission characteristics, thenature of the material and of the element which migrates into the topsurface of the glass from that material being selected in accordancewith the desired change to be induced in the transmissioncharacteristics of the glass.

The molten electrically conductive material forming the elongated body36 may be a metal or a metal alloy and the electrode bar 31 ispreferably of a metal to which this molten metal or molten alloy clings.

A particularly efficacious "antiglare" characteristic is imparted to theglass by introducing lead and copper electrolytically into the upperface of the ribbon 32 of glass and then exposing the modified surface toa reducing atmosphere in the headspace 25 during the continued travel ofthe treated rib bon 32 along the bath 10 of molten metal. This induces agrey coloration and increased reflectivity into the glass. Moltenlead-copper alloy is used for the body 36 of molten material and theelectrode bar 31 may be of platinum or an electrode of ruthenium or ofrhodium plated with platinum. Other metals which can be employed for theelectrode bar 31 with lead or lead alloy as the molten material arepalladium, nickel and copper. An iron electrode bar has also been foundto be advantageous particularly in the form of an iron bar coated withruthenium to which the molten lead readily clings. Further the electrodebar 31 may be of sintered iron to which the molten lead adheres. Otherexamples of suitable metals for the electrode bar 31 are osmium,rhodium, iridium and rhenium.

The molten metal can be introduced between the electrode bar 31 and theglass in the form of minute pellets which are fed into one edge of thebody 36.

When relatively expensive metals are being employed for the locatingmember which have little solubility in the body of molten metal, theymay be in the form of a coating on a suitable base metal or even on arefractory material. For example ruthenium may be plated onto a copper,brass or steel base, or even onto a graphite base. Alternativelyruthenium may be deposited onto a nickel base by vacuum evaporation. Theelectrode may be made of a composite material made from a refractorymaterial such as alumina with a proportion of the desired metal such asruthenium.

Other metals which may be used alone as the body of molten electricallyconductive material 36 are tin, bismuth antimony, indium, zinc andthallium. Indium for example imparts a yellow coloration to the glass.

All these metals have a melting point below l,000 C. so that they can beused over a considerable extent of the ribbon of glass advancing alongthe bath. When it is desired to introduce into the top face of theribbon of glass a metal which is a highly chemically active metal, suchas lithium or sodium, or a metal whose melting point is higher than thetemperatures normally met with in themanufacture of flat glass on thebath of molten metal or a metal with a high-vapor pressure at bathtemperatures, alloys of those metals are employed to constitute the bodyof molten material 36.

The solvent metal must dissolve sufficient of the solute metal to ensurethat current is carried into the glass mainly by ions of the solutemetal. Ideally the solvent metal is relatively inert.

Tin, bismuth or lead may be employed as the solvent metal of the alloydepending on the nature of the solute metal which is to be introducedinto the glass.

For example the body 36 may be an alloy of tin with one of the followingmetals: lithium, sodium, potassium, zinc, magnesium, aluminum, silicon,titanium, manganese, chromium, iron and vanadium.

Bismuth is a particularly useful solvent metal and may be alloyed withany one of the metals: lithium, sodium, zinc, magnesium, aluminum,silicon, titanium, manganese, cobalt, nickel, copper, silver, gold,antimony, indium and rhenium. Bismuth dissolves at least a small amountof many high-melting point metals at the working temperatures of thebath of molten metal and is a relatively unreactive metal.

Lead can be used as the basis of an alloy with any one of the metals:lithium, sodium, zinc, magnesium, aluminum, silicon, titanium,manganese, chromium, cobalt, nickel, copper, silver, antimony, indiumand rhenium.

In the embodiment of FIGS. 1 and 2 the electrode bar or retaining member31 has a length in the direction of advance of the glass ribbon 32(indicated by arrows A in the drawings) which varies laterally acrossthe width of the ribbon 32. Two possible shapes for the electrode bar 31are illustrated diagrammatically in the plan views of F168. 3 and 4.

In FIG. 3 the electrode bar 31 tapers from a maximum length in thedirection of ribbon advance A at the center of the direction at theedges of the ribbon 32. That is, the electrode bar 31 in plan has anoval or cigar shape in profile. Typically the electrode bar may taperfrom a maximum length in the direction A of 3 inches to a minimum of 1inch at each edge of the ribbon 32.

When in use as previously described the electrode bar 31 of FIG. 3causes the body 36 of confined molten material to have a profile in planview which conforms to that of the bar 31. As a result the glass in thecenter of the ribbon '32 is in contact with and receives current fromthe body 36 for a longer period than the glass at the edges of theribbon 32. Consequently the central region of the glass ribbon receivesa larger quantity of the migrating element from the body 36 of moltenmaterial. The resulting glass ribbon drawn from the tank structure wouldhave minimum transmission at its center and maximum transmission at itsedges. To form glass sheets suitable for vehicle windscreens this ribbonis bisected along its longitudinal centerline, so that two componentribbons, each having a minimum transmission region along one edge, areformed: the windscreen sheets are then formed from these componentribbons, the edges exhibiting minimum transmission forming the upperedges of the windscreens.

I claim:

l. A method of manufacturing a pair of float glass component ribbonseach having a shaded characteristic whereby light transmission is aminimum along one lateral margin of the ribbon and increases towards theopposite lateral margin of the ribbon, comprising advancing a ribbon offloat glass along a molten metal bath, maintaining between the uppersurface of the glass and an elongated locating member adjacent to butspaced from the glass an elongated molten metal body clinging to thelocating member, which molten body is effective to produce the desiredshading when metal therefrom is incorporated in the glass surface, theelongated locating member being shaped so that the extent of saidelongated molten body in the direction of advance of the glass isgreatest at the center of the molten body and tapers towards the ends ofthe molten body so that the step of maintaining comprises maintainingthe molten body with a configuration in which its dimension in thedirection of advance of the glass is widest at its center and taperstowards both ends thereof, passing electric current between the moltenmetal body and the bath through the thickness of the glass ribbon toenforce ionic migration from said tapered molten metal body into theglass surface, and cutting the ribbon centrally along its length in thedirection of ribbon advancement.

